In recent years, a car navigation system has spread wherein positional information of a moving vehicle is acquired, for example, by radio waves from an artificial satellite or self-contained navigation and, based on the positional information, for example, map information data, the current position of the vehicle, and a recommendation route to a destination are displayed on a real-time basis.
In utilizing the above car navigation system, however, an expensive device for the car navigation system should be purchased and mounted on the vehicle, and electric wiring should then be carried out. In recent years, an easily removable portable device is on the market. The easily removable portable device, however, cannot be easily purchased by consumers for cost reasons and further requires to ensure a space for mounting the device. In addition, the conventional car navigation system has a problem that the power consumption of the device body is so large that a large burden is imposed on the battery of the vehicle.
Furthermore, in the above car navigation system, the map data is generally supplied in the form of a recording medium such as CD-ROM. Therefore, in order to always use the latest road information which changes momentarily, a recording medium such as CD-ROM, in which the latest map information has been recorded, should be purchased as occasion demands. Therefore, not only the device body cost but also the cost for updating the map information as occasion demands incurs, and, in addition, this involves troublesome work such as updating to the latest map data.
To overcome these problems, a car navigation device, for example, as shown in FIG. 1 has been proposed which reads the latest map data from a predetermined map database through a predetermined transmission medium. FIG. 1 shows a car navigation system described in Japanese Patent Laid-Open No. 255022/1998. This car navigation device is an example of the construction of an information provision system which supplies map data to a car navigation device 7 mounted on a vehicle 8.
In this information provision system, a map data base server 1 storing map data is connected to the Internet 2, and a provider 3, which performs a service of connection to the Internet 2 to users who utilize a public telephone network (a telephone line) 4, is connected to the Internet 2 and the public telephone network (telephone line) 4. A portable telephone base station 5 connected to the public telephone network 4 performs communication with a portable telephone 6 using radio waves as the transmission medium.
In the above construction, the map data, together with the date on which the map data is cataloged in the database, is stored in the database. Further, in the car navigation device 7, the map data, together with date data corresponding to the map data, is stored. The date data in the database is compared with the date data in the car navigation device 7. Based on the results of comparison, the map data and date data in the car navigation device 7 are respectively updated using the map data and date data in the database to update the old map data to new map data.
The conventional car navigation system, however, involves a problem that, even when the update of only old map data is contemplated, an operation for comparison of the date data to update the map is necessary.
Further, the price is high, a space for installation should be provided, and, in addition, the power consumption is large. Due to these disadvantages, the conventional car navigation system has not been extensively utilized.